This randomized placebo-controlled trial evaluated 36,282 postmenopausal women age 50 to 79 years who were enrolled in the Women's Health Initiative (WHI). Participants were randomly assigned to receive 1000 mg of elemental calcium plus 400 IU of vitamin D3 (CaD) daily or placebo for a mean follow-up period of 7 years. NMSC and melanoma skin cancers were ascertained by annual self-report; melanoma skin cancers underwent physician adjudication.

According to researchers, neither incident NMSC nor melanoma rates differed between treatment and placebo groups. However, in subgroup analyses, women with history of NMSC assigned to CaD had a reduced risk of melanoma versus those receiving placebo, which was not observed in women without history of NMSC.

The reduction in melanoma risk for women with history of NMSC, suggests a potential role for calcium and vitamin D supplements in this high-risk group, researchers concluded. “Results from this post hoc subgroup analysis should be interpreted with caution but warrant additional investigation,” they said.